Date: Tue, 3 Aug 1999 13:35:54 +0930 From: Greg Lehey <grog@lemis.com> To: Stephen Hocking-Senior Programmer PGS Tensor Perth <shocking@prth.pgs.com> Cc: hackers@FreeBSD.ORG, shocking@bandicoot.prth.tensor.pgs.com Subject: Re: Adding disks -the pain. Also vinum Message-ID: <19990803133554.S62948@freebie.lemis.com> In-Reply-To: <199908030311.LAA16741@ariadne.tensor.pgs.com>; from Stephen Hocking-Senior Programmer PGS Tensor Perth on Tue, Aug 03, 1999 at 11:11:39AM %2B0800 References: <199908030311.LAA16741@ariadne.tensor.pgs.com>
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On Tuesday, 3 August 1999 at 11:11:39 +0800, Stephen Hocking-Senior Programmer PGS Tensor Perth wrote: > The people who I work for were about to junk a bunch of 6 year old disks when > I snaffled them. Among them were 4 DEC DSP5400S (3.8GB each), with a nice > external case. These disks had been doing duty on a boat carrying out seismic > surveys, attached to misc. Sun workstations. These are typical of their > vintage - full height 5 1/4" drives fast narrow SCSI2, and noisy as all > blazes. I have them hooked up to a NCR810, as one striped FS (it's just for > experiments, not valuable data). fdisking them was easy, but disklabelling > them was a royal pain. I ended up editing the /etc/disktab file to add an > appropriate label and running "disklabel -w -B /dev/rda0c DSP5400S" which > still gives an error message, but appears to install the label. I only found > out that it installed the label by accident, wasting a bunch of time in the > process. Did you try 'disklabel -w da0 auto'? > I created a striped volume across the 4 drives with the default stripe size of > 256K. I read the rather interesting discussion within the man pages about the > optimal stripe size and have a couple of queries. Firstly, the type of traffic > that this 13.9GB filesystem will see will be mainly sequential reading and > writing of large files. There will only be a few files (~2-30), each several > gigs. (I'm fooling around with the seismic software at home, and typcal > surveys can results in files many gigs in size). Given that FreeBSD breaks > I/Os down into 64k chunks, would having a 64k stripe size give more > parallelism? No, it would cause a higher I/O load. Vinum doesn't transfer entire stripes, it transfers what you ask for. With a large stripe size, the chances are higher that you can perform the transfer with only a single I/O. > I'm seeing 4.4MB/s if I read from an individual disk, but only about > 5.6MB/s when reading from the striped volume. How many concurrent processes? Remember that striping doesn't buy you anything with a single process. You might like to try rawio (ftp://ftp.lemis.com/pub/rawio.tar.gz) and see what that tells you. > Looking at the systat display, the 8k fs blocks do seem to be > clustered into larger requests, so I'm not too worried about the FS > block size. What have people observed with trying larger FS block > sizes? I don't know if anybody has tried larger FS blocks than 8 kB. I once created a file system with 256 kB blocks (just to see if it could be done). I also tried 512 kB blocks, but newfs died of an overflow. I'd expect that you would see a marked drop in performance, assuming that it would work at all. Greg -- See complete headers for address, home page and phone numbers finger grog@lemis.com for PGP public key To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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